Influence of proline‐14 substitution on the secondary structure in a synthetic analogue of alamethicin

Due to the bend introduced by proline 14 in the conformation of alamethicin (AcUPUAUQUVUGLUPVUUEQFol), the role of this residue was assumed essential in the barrel-stave model for voltage-gated ion channels. Taking advantage of a previous synthetic alamethicin analogue (L2) in which all eight α-aminoisobutyric(U) Were replaced by leucines (AcLPLALAQLVLGLLPVLLEQFol), another analogue (L5) was synthesized in order to test the effects ofproline-14 substitution by an alanine (AcLPLALAQLVLGLLPVLLEQFol). Previous conductance experiments showed that both high voltage dependence and multistate behavior were conserved. In order to complement these functional results, a conformational study of L5 has been undertaken and compared to L2 using CD. high field nmr, and molecular dynamics. Results show that L5 presents a better ordered structure than L2 particularly in the region of the substitution and in the C-terminal part. These results are discussed as regards the previous hypothesis of the nonessential character of helix bending for the gating of voltage-dependent ion channels. © 1995 John Wiley & Sons, Inc.